Stabilized sight system employing autocollimation of gyro-stabilized light beam to correct yaw and pitch orientation of coupled sight line and servo system mirrors



ING AUTOCOLLIMATION OF -S'I'ABILIZED LIGHT BEAM TO CORRECT YAW AND FITCH Sheet of 2 R. H. Mau-:R STABI'LZED SIGHT 'SYSTEM EMYLOY GYRO ORIENTATION Ol" COUPLED S [GNT LTNL' AND SERV@ SYST'M MIRRORS M4036 XF? may 27, 1969 Filed Sept.V 22, 1965 Mmm 1:"

R. H. MEIER 3,446,9@0 STABILIZED SIGHT SYSTEM [IMPLOYING AUTCJCOLLIMATION OF GYRO-STABILIZED LIGHT BEAM TO COI RECT YAW AND FITCH NTATlCN OF COUPLPID SIGHT L'NE ORI May 27, i969 SYSTEM MIRRORS Sheet AND SERVO Filed Sept. 22,' 1965 @domweg 'linited @rates ILS. Cl. Z50-231 2 Claims ABSTRACT OF THE DISCLOSURE Stabilized sight system employing a stabilized light beam which is reflected from an autocollimating mirror and returned to a photosensitive detector. When the orientation of the system changes, the beam is displaced from the ccner of the detector, producing an error signal which directsscrvos to rotate a second mirror to return the beam to the center of the-detector. The opposite side of the second mirror is in the path of the line of sight so that the line of sight will be simultaneously retained to its original position.

This invention relates to optical sight systems and more particularly to a line of sight stabilizing system in which a sight line reflecting mirror is gyroscopically stabilized about azimuth and elevation axes.

Certain armament systems employ an optical sighting` device such as a manually operated telescope or periscope in which a crosshair reticle is trained manually on a target. The launching or guidance system for the projectile or missile tired by the system is coordinated with the sighting system so that the missile will strike the target which i-s centered in the reticle. Nol diiliculty is encountered so long as the armamentV system is positioned on a fixed platform. i

However, in advanced armament systems of the type wherein a missile may be tired'from a moving airborne vehicle or ground vehicle,'it is necessary to provide motion compensationv means in the sighting system for overcoming the motions of the vehicle. If, for example, the sighting device is mounted in an aircraft or tank, motions such as pitch and yaw affect the line of sight and must be compensated.

It is not practical to overcome the problems caused by vehicle motion-by stabilizing the sighting means with a gyroscope or the like. This is because when a sighting system is stabilized with respect to the distant target, the eyepiece of the sight will move with respect to the moving vehicle, and hence with respect tothe eye of the observery who sits in the moving vehicle. This relative motion be tween the observer and the eyepiece makes sighting dithcult. Furthermore the inertia of the sighting system .pre-

vents exact compensation for vehicle motion and introduces some deviation between the optical axis of the sighting device and thc desired target.

Prior art systems which stabilize an internal component system which senses deviations of thc line of sight from a gyro spin axis and which applies correction signals to the line of sight system Without the use of mechanical transfer mechanisms. l

Extremely accurate measurement of the deviation of the line of sight from the gyro spin axis is obtained by the optical detection system; correctionsV are accurately and `quicltly applied by means of an electrical servo to the line ot sight system.

it is therefore another object of this invention to provide a gyroscopically-controlled optical sight system which utilizes optical means todetcct deviations of the line of sight from the gyro spin axis. g It is still another object of this invention to provide a gyroscopically-controlled optical sight system in which the stabilizing gyro utilizes an electro-optical detector to provide signals to the optical sight system to compensate deviations in azimuth and elevation.

DRAWINGS SUMMARY VAccording to a principal aspect of the invention, a gyro-stabilized sight system is provided within a vehicle for maintaining the line of sight of the system in corre spondence in azimuth and elevation with the spin axis of the gyro. A sight line dcflccting mirror movable with respect to the vehicle has a reflecting front surface disposed in thc line of sight optical system. An optical path system for` measuring displacement of the line of sight from the gyro spin axis is provided which includes a source of light disposed along the gyro spin axis and an autocollimating mirror. The reflecting back surface of the sight line detlecting mirror is disposed to project a collintated beam of light from the light source onto the autocollimating mirror which reflects a return beam to an optical detector by way of the rear surface of the line of. sight deilecting mirror. The detector is disposed along the gyro spin axis and is mounted on thc gyro for stabilization in space. The displacement of the return beam from the gyro spin axis is measured by the stabilized detector which provides azimuth and elevation error signals indicative of the deviation of the line ot sight from the gyro spin axis. Closed loop servo means responsive to these deviation signals move thc sight line dcllecting mirror in a direction to cause the line of sight to correspond to the gyro spin axis.

FIGURE l FIGURE l s hows a stabilized line of sight system for controlling aline of sight l1 between a sighting telescope 'l2 anda target 13. The liuc of sight 1I is directed along an optical path from thc telescope l2, to a reflecting mirror 14, to a sight liuc detlecling mirror 1S, and thence to the target 13. lvlirror I4 and telescope 12 are fixed to the vehicle while mirror 15 is movable with respect thereto. Mirror l5 has a reflecting front surface r1 in thc` optical path of the line of sight il. anda reflecting back surface b which is parallel to front surface n.V The sight line deilecting mirror .l5 is mounted in a suitable frame which is pivotcd about the elevation axis by means of a shaft (not shown) which is driven by a pitch torque motor 17. The shaft for pivoting mirror l5 is`journalled on the upper portion of a gimbal ring 1.9 which is mounted is done by means of a system including a gyroscope 22i of conventional two-axis type which provides stabilization in space about its spin axis 23. Gyroscope 22 has a housing 16 attached by suitable means to the vehicle plat form. A gyro rotor 24 is mounted on gimbal means 29 so that it is free to rotate about spin axis 23. Gimbal means 29 is part of a conventional two-axis gimbal which is supported by housing 16. Rotor 24 has a primary mir ror surface 25, a secondary mirror surface 37, and a negative lens assembly 36. Gyro 22 has a pair of precession coils 26 and 27 for torqueing the gyro in accordance with a control 30 which maybe, for example, operated by hand by the operator to select the target 13 viewed through the telescope 12. 1n this manner, gyro spin axis 23 may be displaced inlr accordance with operator'commands.

An optical light path system is provided for detecting deviations of line of sight 11 from gyro spin axis 23 in order to develop correction signals for the pitch motor 17 and yaw motor 21. The detection system includes a light detector 28 which is attachedl to an inner (yaw) gimb'al 29 and which is stabilized by the gyro along spin axis 23.

Detector 28 is sensitive to light and comprises a plurality of separated surfaces as shown in FlG. 2. Detector 28 has a central opening 31 which passes light directed from a source 32 through a lens 33.

Light source 32 and lens 33 are fxedly attached to the gyro housing 16. Source 32 projects a light beam through an opening 41 in the housing 16 to optical fibers 34 which direct the light beam through an opening 31 to the mirror system which includes negative' lens 36, see- Ondary reflecting mirror-37, and primary mirror 25. The light beam is collimated by the Vmirror system and projected along axis 23 onto the back surface b of mirror 15. The collimated beam is reflected by mirror 15 onto an autocollirriation mirror 39 which is attached to gimbal 19 and is movable therewith about the azimuth axis.

The return beam from the mirror39 is again reflected by surface b of mirror 15 and is focused on detector 28 by means of mirrors 25 and 37 and lens 36. .Detector 28, which is positioned to receive a slightly unfocused image, provides electrical' output signals to an error detection circuit 43; these signals indicate azimuth and elevation deviations of the line of sight 11 from the gyro spin axis 23.

Circuit 43 provides signals to yaw motor 21 and pitch motor 17 which thereupon correct the orientation of mirror 15 in azimuth and elevation.

Since the front and back surfaces a and b of mirror 15 are parallel, the deviationof the light path reflected 4by back surface b from the beam received by detector 28 is an exact measurement of the deviation of the line of :release tion of axis 23 with respect to surface b of mirror 15 is reflected as a four fold change in position of the light r spot in detector 28.

sight 11 from the gyro spinaxis23. Therefore orientation l ,every degree of deviation of mirror 15, line of sight deviation is changed by two degrees.

The autocollimation technique, wherein the light beam is collimated bythe optics of the gyro, projected on autocollimation mirror 39, and then returned to detector 28, provides a very high sensitivity to deviations of the line of sight; 11 from the gyro spin axis 23. Any change of posi- The optical sight 'line of sight 11 may be readily displaced at the command of the operator by control 30 which torques gyro 22 by means of precession coils 26 and 27. The resultant displacement of spin axis 23 will be sensed b y detector 28; mirror 15 will thereupon be p controlled by the servo system to follow spin axis 23.

FIGURE 2 4to the vehicle. Ordinarily the reflected light beam will be coincident with the central opening in detector 28. However, vehicle motions cause the collimatcd light beam from the optical path detection system to be reflected from the surface b of mirror 1S at an angle Vwhich direets the returned beam to one of the quadrants A, B,

C, or D (or the boundary between adjacent quadrants) which results in an output from the detector 28. Signals from each of the surfaces A, B, C, and D of detector 28 are fed to an amplitude modulation system which includes a preamplifier 47 and a demodulator 48 for each of the detector surfaces. The output of the demodulators is vfed to summing means 49 which supplies a first .signalv to pitch motor 17. This signal is indicative of the elevation deviation of mirror 15 and therefore the deviation of line of sight axis l1 from gyro spin axis 23. Summing means 49 also supplies a second Signal to yaw motor 19; this signal is indicative of the azimuth deviation of line of sight axis 11 from gyro spin axis 23. Detector 23 is placed at a slightly out of focus position so that when no deviation is encountered, the output of each of its segments will be the same and proportional to one-quarter of the energy of the light beam autocollimated on detector 28. Thedeteetion system thus operates as a nulling closed-loop servo which eliminates linearity problems inherent in position slaving devices of the type where the servo loo'p operates at other than a zero position of two' readout devices.

The stabilization system of the invention operates over wide frequency ranges of line of sight fluctuations, forexample, for fluctuations of t) to 20() eps. Sight line stabilization operates according to classical closed loop servo theory; that is, an error signal is generated and the mirror is torqued by the yaw and pitch torque motors in response to the error .signal4 to cancel the error, thereby returning the system to a .null position wherein the sight line axis will be coincident with the gyro spin axis.

FIGURES su AND 3b PIGURES3t1and 3b illustrate means for balancing both statically and dynamically the stabilizing mirror 15 around each of the gimbal axes. Balancing wheels 61 and 62 are mounted on a line parallel to the yaw axis. Balancing wheel 61 is mounted on the pitch axis and is lixedly attached to the stabilizing mirror 1S; Balancing wheel 62 is mounted in rolling contact with wheel 6l with bearing friction provided by thin steel crossed bands (not shown) which are connected to both whels. Wheels 61 and 62 have the same radius and hence tend to rotate through the same angle, but in opposite directions, when the vehicle platform moves through a given angle. Wheel 62 has one-third the polar moment of inertia of the combined inertia of wheel 61 and mirror 15. Since wheels 61 and (2 are mounted in rolling Contact, each motion counteracts the other and stabilizing mirror 15tends to rc main fixed relative to the vehicle frame. Since wheel 61.

and mirror l5 move through one-half the unity angular reference of the platform angle, torque balancing is achieved. ln this manner inertial balancing of the stabilizing mirror is maintained during vehicle motions.

While'there has been described what is-at present considered to be the preferred-embodiment of the invention `it will be apparent that various modifications and other point on said'platform to44 said point in space, said means including a rst mirror havingrellecting front and back surfaces, said front surface being disposed in the path of said line of sight,

(b) means,l including a light source and a gyroscope having a rotatable'element with a reflecting surface, for providing a light beam which is directed at the back surface of said first mirror and whose position is stabilized in space along a given axis, the light from said source illuminating said reflecting surface and being reflected therefrom to said back surface v of said rst mirror,

(c) detector means fixed to said platform and having a photosensitive surface divided into at least four electrically isolated regions and positioned to receive said beam after its reflection from said back surface of said first mirror and to provide a plurality of elec trical outputs indicative of the position at which said beam impinges said photoserisitive surface,

(d) means, comprising yaw and pitch motors, for changing the orientation of said first mirror with respect to said platform according to the 4outputs of said detector means, and

(e) a second mirror fixed to said platform and arranged to receive Said light beam, after reflection from saidback surface of said first mirror, and to refiect said received light beam to said back surface, said back surface then re-retlecting said beam,

(f) said detector means having an aperture in a central portion of said photosensitive surfoce thereof` and being positioned so that said given axis'passes through saidV aperture and so that said photosensitive surface lies in a plane orthogonal to said given axis and receives said reflected beam.

6 il. A sight system for stabilizing a line of sight from a point on a movable platform to a point in space despite motion of said platform, said sight system b'einig7 of the type which comprises:

(a) means for establishing a line of sight from said v point on said platform to said point in space said means including a first mirror having i'ellectingfront and back surfaces, said front surface being disposed inthe path of said line of sight, t

(b)` means including a light source and a gvroscope having rtl rotatable element with a reflecting;surface, for providing a light beam which is directed at the back surface of said first mirror and whose position is stabilized in space along a given axis, the light from said source illuminating said reflecting surface and being reflected therefrointo said back surface of said first mirror, r

v (c) detector means fixed to said platform and having a photosensitive surface divided into at least four electrically isolated regions and positioned to receive said beam after its rctlection from said back surface of said first mirror and to provide a plurality of electrical outputs indicative of the position at which said beam impinges said photosensitive surface,

(d) means, comprising yaw and pitch motors` for changing the orientation of sai'd first mirrorfwith respect to said platform according lo thc outputs of said detector means, and

(e) a second mirror fixed to said platform and arranged to receive said light beam, after reflection from said back surface of said first mirror, and to reflect said light beam to said back surface. i

(f) means, comprising said back surface, for directing said beam to said photosensitive surface of said detector means,

(g) said detector means having an aperture in a central portion of. said photosensitive surface thereof and being positioned so that said given axis passes through said aperture and so that said photosensitive surface .lies in a plane orthogonal to said given axis.

References Cited UNITED STATES PATENTS ROBERT SEGAL, Primary Emmi/ier. 

